Manufacture of fumaric acid



Patented Nov. 23,

UNITED STATES PATENT OFFICE Louis H. Howland, Watertown, and William F. Brucksch, Jr., Bethany, Conn., assignors to United States Rubber Company, New York N. Y., a corporation of New Jersey No Drawing. Application April 27, 1946, Serial No. 665,631

6 Claims.

This invention relates to the conversion of cis alpha-beta unsaturated carboxylic acids to their trans isomers, and more particularly of maleic acid to fumaric acid. An object of this invention is to provide a catalytic means whereby the cheap and abundant maleic anhydride is easily and readily converted into fumaric acid.

It is known that the isomerization of maleic acid to Iumaric acid is accelerated by various inorganic materials such as iodine, bromine, hydrochloric acid, hydrobromic acid, sulfuric acid, potassium thiocyanate, sodium bromide and ammonia. Pyridine has also been observed to catalyze the rearrangement. For a proposed mechanism of the isomerization and a discussion of the prior art, reference is made to the publication of Nozaki and Ogg in Journal American Chemical Society, 63, 2583 (1941), and of Nozaki, ibid 63, 2681 (1941). As pointed out by these authors, the catalysts used for the isomerization of maleic acid are equally usable for the cis-trans isomerization of all alpha-beta unsaturated carboxylic acids. The same is true of the catalysts of this invention.

The present invention relates to the discovery that thioamides as a class are capable of accelerating the conversion of maleic acid to fumaric acid. The thioamides contain the structural nucleus where the free valences are attached to hydrogen or any organic radical, and R is hydrogen or any organic radical attached to the thiocarbamyl group by a carbon atom. Representative examples containing the above structural feature are: thioformamide, thioacetamide, thiopropionamide, thiobutyramide, thiovaleramide, thiododecyiamide, thiobenzamide, thionaphthamide, thioacrylamide, thio-N-methyl-acetamide, thio-N,N- dimethyl-acetamide, thio-N,N-diethyl-acetamide, and thio-N-cyclopentamethylene-benzamide.

The conversion of maleic acid to fumaric acid is conveniently carried out in water solution at an elevated temperature. Fumaric acid being relatively water-insoluble separates as soon as its. concentration exceeds its solubility. At the end of the isomerization the water mixture is cooled, filtered and the fumaric acid purified by washing with water or digestion with 1 N-hydrochloric acid. The yield of the fumaric acid is dependent upon the concentration of the maleic acid, the

amount of catalyst, and the temperature of the conversion.

In general, a temperature of at least 50 C. should be maintained, and preferably the tem- 5 perature should be at or slightly below the boiling point of the water solution. Stirring is recommended to prevent bumping and spattering caused by the suspended fumaric acid. The optimum concentration of the maleic acid for each thioamide can be determined experimentally by adding 2% of the thioamide to a gently boiling aqueous solution of maleic acid based on the total weight of solution and refluxing for 2 hours. The reaction mixture is then cooled, diluted with water, filtered. and the separated fumaric acid washed with water and dried. The preferable maleic acid concentration usually lies in the range of 40-60%. Above about 60% maleic acid concentration, the yield decreases.

The amount of catalyst necessary can be varied over a wide range generally from 0.1 to 5% based upon the tota. concentration of the maleic acid solution. If the catalyst is particularly vigorous, it may be added gradually as a powder, or as a 25 concentrated water solution.

The following table lists the yields of fumaric acid-obtained by the addition of 2 grams of the catalyst to a gently boiling solution of 60 grams maleic anhydride in 40 grams water and heating for 2 hours,.c0oling, diluting with water, filtering, and drying the fumaric acid.

- air" le Catalyst Fumaric Acid Thioacetamide 56.8 Dithiooxamide 30.0 Thiopropionamidc 34. 2 Thioacetanilide 20. 6 Thiobenzanilide l7. 4 4 Blank 0.0

Having thus described our invention, what we claim and desire to protect by Letters Patent is:

1. A method of converting a cis-alpha-beta unsaturated dicarboxylic acid to its trans isomer which comprises heating it to at least 50 C. in an aqueous medium in the presence of a thioamide oi the formula s R-- -N\ where X is a radical from the class consisting of hydrogen and hydrocarbon; B being a radical from the class consisting of hydrocarbon and thiooxamide.

2. A method of converting a cis-alpha-beta unsaturated dicarboxylic acid to its trans isomer which comprises heating it to at least 50 C. in an aqueous medium in the presence of a compound of the formula s ri -NH.

where R is a hydrocarbon group.

3. A method of converting a cis-alpha-beta unsaturated dicarboxylic acid to its trans isomer which comprises heating it to at least 50 C. in an aqueous medium in the presence of a compound of the formula I Bil-NH! where R is an aliphatic hydrocarbon group.

4 4. A method of converting a cis-alpha-beta unsaturated dicarboxylic acid to its trans isomer which comprises heating it to at least C. in an aqueous medium in the presence of thioacetamide. 5. A method of converting a cis-alpha-beta unsaturated dicarboxylic acid to its trans isomer which comprises heating it to at least 50 C. in an aqueous medium in the presence of dithiooxamide. 6. A method of converting a cis-alpha-beta unsaturated dicarboxylic acid to its trans isomer which comprises heating it to at least 50 C. in an aqueous medium in the presence of thiopropionamide.

LOUIS H. HOWLAND. WILLIAM F. BRUCKSCH, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,404,103 Scott July 16, 1946 OTHER REFERENCES Clemo et al., Jour. Chem. Soc." (London), Pt. 1 (1930), pages 213, 214, 215. I

Taube, J. Am. Chem. Soc, vol. 65, page 526 (1943). 

